This invention relates to multi-speed planetary transmissions and, more particularly, to a family of multi-speed planetary transmissions having six torque-transmitting mechanisms, and three planetary gearsets to produce a minimum of seven forward speed ratios and one reverse speed ratio.
Automatic shifting power transmissions are currently used in a majority of the vehicles produced in the United States. These vehicles generally employ three- and four-speed power transmissions. More recently, a trend towards more ratios, such as five- and six-speed power transmissions, has been proposed. In fact, some manufacturers do provide five-speed transmissions. Many of the vehicles utilizing manual type transmissions or countershaft type transmissions employ five- and six-speed power transmissions.
The five- and six-speed power transmissions provide improved vehicle acceleration performance and fuel economy when compared with three- and four-speed transmissions. Seven-speed transmissions offer further vehicle acceleration performance and fuel economy improvements over five- and six-speed transmissions. However, seven-speed power transmissions have not been proposed due to the complexity of these assemblies, as well as size and cost. There are many current patents that describe five- and six-speed power transmissions. Some of the six-speed power transmission patents, especially those assigned to the assignee of the present invention, describe six-speed power transmissions in families, wherein one or more family members incorporate a limited number of seven-speed power transmissions.
It is an object of the present invention to provide an improved family of multi-speed transmissions providing at least seven forward speeds.
In one aspect of the present invention, each family member includes three planetary gearsets and each planetary gearset has three planetary members.
In another aspect of the present invention, each family member has six torque-transmitting mechanisms represented by five rotating type torque-transmitting mechanisms and one torque-transmitting mechanism that is either of the rotating type or the stationary type.
In yet another aspect of the present invention, members of the first planetary gearset are not continuously interconnected with members of the second or third planetary gearsets.
In yet another aspect of the present invention, a first member of the second planetary gearset and a first member of the third planetary gearset are continuously interconnected by an interconnecting member.
In yet still another aspect of the present invention, a second member of the third planetary gearset is continuously connected with a transmission housing.
In still another aspect of the present invention, the output shaft is continuously interconnected with at least one member of the planetary gearsets.
In still another aspect of the present invention, the input shaft is not continuously interconnected with any member of the planetary gearsets.
In still another aspect of the present invention, at least two of the torque-transmitting mechanisms operate as input clutches that are selectively connectible between the input shaft of the transmission and at least one member of one of the planetary gearsets.
In yet still another aspect of the present invention, a third of the torque-transmitting mechanisms interconnects a member of one of the planetary gearsets with the output shaft, or another member of one of the planetary gearsets.
In a further aspect of the present invention, a fourth of the torque-transmitting mechanisms selectively interconnects a member of the first planetary gearset with a member of the second or third planetary gearset.
In a yet further aspect of the present invention, a fifth of the torque-transmitting mechanisms selectively connects a member of the first or second planetary gearset with another member of one of the planetary gearsets.
In a still further aspect of the present invention, a sixth of the torque-transmitting mechanisms selectively interconnects a member of one of the planetary gearsets with either another member of one of the planetary gearsets or with the transmission housing.
In yet still a further aspect of the present invention, the six torque-transmitting mechanisms are selectively engaged in combinations of four to establish at least seven forward speed ratios and one reverse speed ratio between the input shaft and the output shaft of the transmission.
The present invention is represented in a family of planetary transmissions that are low content seven speed mechanisms in that only three planetary gearsets and six torque-transmitting mechanisms are needed to establish these seven forward speed ratios. Each of the planetary gearsets has a sun gear member, a ring gear member, and a planet carrier assembly member. One defining feature of the transmission family members is that a member of one of the planetary gearsets is continuously interconnected with a member of another planetary gearset. Further, a member of one of the planetary gearsets having an interconnected member also has a member continuously connected to a transmission housing.
The family of transmissions is further defined in that at least one member of one of the planetary gearsets is continuously interconnected with the transmission output shaft and the transmission input shaft is only selectively connectible with members of the planetary gearsets through two independently selectively engageable torque-transmitting mechanisms. Four remaining torque-transmitting mechanisms provide selective interconnections either between the planetary members of at least two of the planetary gearsets, or between planetary gear members and the transmission housing. The six torque-transmitting mechanisms are selectively engageable in combinations of four to establish at least seven forward speed ratios as well as at least one reverse speed ratio. An attractive feature of this family of transmissions is that by engaging four torque transmitting mechanisms for each speed ratio only two torque transmitting mechanisms remain open which minimizes the spin loss of the transmission.